What is the difference between land photography and underwater photography? If I had ten dollars for every time I have been asked that simple question over the years, I would be in the market to buy a new camera.

There is not one simple answer to the question, but let's begin with the subject of lighting.
I'll take it for granted that the reader has a fundamental grasp of lighting principals in our topside world. My main purpose is to apply these primary rules in an underwater setting, although many of the facts can be cross referenced back into above water applications.

Apart from the fact that there is additional training involved in the form of a scuba certification course to shoot underwater pictures, the main difference is in understanding lighting and what effect the water has on it's basic properties.

Although my area of expertise is underwater videography, the same set of rules apply to still photography as well as to video. So understanding what happens to the available light below the surface is the biggest step in the learning process.

Air is essentially a transparent environment which allows light to travel through it relatively unhindered. On the other hand, water is approximately 800 times denser than air which forces light to travel at a much slower speed. It also scatters the light as it loses color and intensity.

These properties and behavior of light underwater create special problems for the photographer and consequently necessitate a modification of certain photographic principals.

REFLECTION.

For sunlight to be utilized in taking pictures underwater, it must first penetrate the water's surface. However, the uppermost layer of the ocean acts like a barrier to the light rays causing them to bounce back into the atmosphere. How much light is reflected is dependent on the position of the sun and also the condition of the seas.

When the sun is directly overhead at midday, reflection is minimal. Early morning and late afternoon when the sun is nearest the horizon, light must penetrate the water surface at an extreme angle and reflection is greatest. Also rough seas will reflect more light than calm waters as a result of adding many more reflective surfaces on the edges of the waves.

Therefore, the best time and conditions with the best light for underwater photography is between 10.00. am until 2.00. pm on a bright, windless, cloudless day.

REFRACTION.

As light rays travel underwater, they undergo a modification in their direction. As a result of the change in density between air and water, light rays are refracted, or bent. This results in an optical illusion which some people are already familiar with. The fact that objects will appear about 25% closer than they actually are.

This apparent distance is what we and the camera lens see as opposed to the actual, or measured distance. For example, if the soft pink coral appears to be three feet away from you (apparent distance), it is actually four feet away (measured distance). This is very important when we consider that the lens sees apparent distance only and to achieve a sharp, clear picture we must set our focus accordingly.

The next consideration is that objects will appear larger than they actually are. An image underwater is magnified by about one third, so a fish that appears to be three inches long is actually only two inches long.

The pen in a glass of water is an often used demonstration of the visual effects of water. Note how the portion of the pen in the water seems (appears) larger and closer than the portion in the air.

ABSORPTION.

Now we have to consider the color qualities of light. Direct light from the sun is called white light. Though it appears to have no color, it is actually composed of all the colors in the spectrum. If you were to project it through a prism, you would see it break up into bands of color. Each color is a wavelength of light. Most people will remember this experiment from chemistry class at school.

When we descend below the surface, water absorbs the wavelengths of light selectively, one by one as depth increases. Though exact absorption rates will vary depending upon water conditions, you can assume that red will disappear at a depth of around 15 to 20 feet, orange at between 25 to 30 feet, yellow at 45 to 60 feet, green at 70 feet and at 100 feet, everything will appear blue or grayish green. At extreme depths all the light will be absorbed and everything will appear deep blue or black.

The loss of color is deceiving. The human brain compensates for much of the color loss and even at depths below 30 feet, your eyes will still see some red. But a fact which we must understand is that the camera is really dumb. It has no brain, so therefore it will not compensate. To overcome this problem, artificial light sources must be used.

HORIZONTAL COLOR LOSS.

Progressive color loss is not a function of depth but is dependent on the distance light travels through water in any direction. The greater the distance light has to travel through water, the more color will be absorbed. For ambient light to strike your film or video tape, it first travels vertically through the water column to your subject. It then reflects off your subject and travels horizontally to the camera and through your lens to the film.

Let's just say you are shooting at a depth of 10 feet and the critter you are aiming at is four feet away. This means that the light has to travel a total distance of 14 feet. As a result, most of the warm colors will be filtered out. A vivid colored fish will look a dull green or brown color.

The best way to obtain bright, natural colors underwater is to get close to your subject and to use an artificial light source such as a strobe for photography and 100 watt light heads with a diffuser for videography. Always remember. When light travels through water, it is traveling through a filter. The greater the distance the light must travel, the more the image will be degraded by the filter (water). The objective therefore is to reduce the amount of water separating subject and camera. So once again, get as close as the creature will allow.

ADD ON FILTERS.

In addition to lighting our subject, there are a variety of 'add on' filters we can use to increase our results. These color correctors assist the ambient light in re introducing the warm colors onto our film or tape. When working in water with a greenish tinge, as in the west coast of our continent from Seattle north to Vancouver Island, a magenta filter will produce good results. For blue caribbean waters, I always prefer my red color correction filter. My best advice to a beginner would be to start out with the UR Pro red color correction filter. There are other brand names on the market, but the UR Pro is the most forgiving.

BACK SCATTER.

While the strobe or video light solves one problem, that of color filtration, it creates another problem known as back scatter. Back scatter looks like snow or dust in your photograph or video footage. In extreme cases, it will appear like blurry hexagons. It is actually neutrally buoyant particles of sand, plankton, algae and other organic matter suspended in the water. When the strobe is fired, the particles act like thousands of tiny mirrors reflecting the light back to the lens. The resultant exposure is not only marred by grayish specks but is lacking in finite detail and richness of color.

In the videography application, back scatter can be reduced by insuring that the talent keeps his or her fins clear of the bottom. In addition to this, when practicing underwater still photography, positioning the strobe off to one side will reduce the back scatter problem. This technique will insure that the light intensity is not between the lens and the subject. If we leave these suspended particles alone and refrain from illuminating them, they won't spoil our picture. After all, our only intention is to throw light on the subject, not the water in between.

POST PRODUCTION FILTERS.
As in topside video work, occasionally we misjudge the lighting conditions and must attempt a repair within Final Cut Pro. There are a few filters in the browser which I have discovered work well with underwater video footage. The Proc Amp filter can be used to put some vibrancy into an otherwise washed out shot. The RGB Balance filter is another which if used sparingly can save an otherwise interesting piece of footage from the cutting room floor.

But these filters are definitely no substitute for getting it right in the first place. The best angle of attack is to concentrate on the basic principals of lighting so that your footage can go untouched from the camera to the timeline.

In this small article, we have only brushed the surface (no pun intended) of the basic principals in lighting a subject underwater. The reader must realize there are quite a few other areas to consider in the quest to reproduce good quality images on film or video, both above and below water. But in mastering the lighting principals, we have taken an enormous step in the endeavor. Good hunting and remember the ultimate tip. After you've mastered all the rules, dare to break them.

Ian Sutherland is the owner of Gaelic Digital Video Productions. His TV series Planet Ocean can be seen on Shaw Cable 11 in Winnipeg, Manitoba, Canada. Individual episodes of the series are available by contacting Ian at his e-mail address.